The present invention relates generally to radiotelephone communications systems, and more particularly to an improved method and apparatus for assigning duplex radio channels and scanning duplex radio channels assigned to mobile and portable radiotelephones in cellular radiotelephone communications systems.
Prior art radiotelephone communications systems typically included a single, high power base station for covering a large geographical service area, for example, a large city and its surrounding metropolitan area. The base station was centrally located and included a plurality of duplex radio channels for providing communications paths to radiotelephones anywhere in the system. Supervision of the radio channels was relatively simple and was typically performed by a centrally located control terminal. However, the expansion of service in such radiotelephone communications systems was limited since additional radiotelephones could only be accommodated by adding more duplex radio channels, the availability of which is limited and controlled by governmental regulation.
In order to increase the capacity of radiotelephone communications systems, the geographical service area of some radiotelephone communications systems was divided into a plurality of cells, each of which included a base station having a plurality of duplex radio channels. Since the transmitters of such base stations were operated at relatively low power, duplex radio channels could be reused in geographically separated cells, thereby allowing a limited number of duplex radio channels to serve more radiotelephones than possible with prior radiotelephone communications systems having only one centrally located base station.
However, supervision of the radio channels in such cellular radiotelephone communications systems is complex and requires sophisticated control circuitry since there are large number of base stations and it is necessary to provide the capability of transferring a radiotelephone from one duplex radio channel to another when the radiotelephone moves from cell to cell. Accordingly, there exists a need for improved techniques and processes for controlling communications paths to radiotelephones in cellular radiotelephone communications systems.